The present invention relates to a method and apparatus for determining and extending a change interval for an operating fluid of a unit, comprising the steps of evaluating at least one operating variable representing a qualitative condition of the operating fluid, and continuously calculating therefrom the change interval.
DE 40 38 972 C1 describes a device for calculating a motor-vehicle service interval in which it is possible to precisely calculate a service interval and indicate the necessity of a vehicle inspection to the driver. This known device also makes it possible to extend the service interval thus calculated once by a defined time period or a defined vehicle mileage, i.e. to postpone the next time of inspection as long as an engine-oil addition process has taken place beforehand.
This conventional approach is obviously based on the realization that, although partial replacement of the spent engine oil does not bring about an optimum condition, it does nevertheless guarantee sufficiently reliable engine operation. Particularly in the transportation of goods over long distances by truck or lorry, it is thus still possible to make one or more urgent deliveries reliably before finally bringing the lorry concerned in for inspection. In other words, this automatic one-off extension of the normal service interval means that there is no need for the driver on a freight-hauling trip, for example one which takes him abroad, to feel obliged to carry out the necessary servicing work there and then, on illumination of the relevant warning light. On the contrary, the addition of engine oil or the partial replacement of the spent oil is sufficient to allow him or her to reach home base without difficulty. The step of adding engine oil thus evidently extends the expired service interval on a one-off basis by a defined period of time or a defined mileage, with the calculation of the service interval being based on the qualitative condition of the engine oil.
No account, however, is taken in the known device of the fact that the time at which the change interval determined for the operating fluid (e.g., engine oil) falls due does not in general coincide with the time at which other unit service intervals fall due, for example those service interval times for such units as the brakes, the gearbox, the steering, the suspension etc. As a result, service work in, for example, a vehicle is undertaken at different times, resulting in a plurality of out-of-service periods.
An object on which the present invention is based is therefore to provide a method in which the out-of-service period of the unit does not result from the qualitative condition of the operating fluid.
This object has been achieved in accordance with the present invention by a method and apparatus which operate such that the continuously calculated change interval is related to a specified unit service interval and, if the change interval expires before the service interval, a regeneration signal for removal of a quantity of the spent operating fluid and the replacement of said quantity with a fresh operating fluid is produced as a function of the difference therebetween.
The present invention is based primarily on the discovery that it is possible, by controlled quantitative removal of the regenerable operating fluid in dependence on its qualitative condition and its regeneration by replacing the quantity removed with fresh operating fluid, to extend the change interval thereby, on one hand, allowing the change interval for the operating fluid to be adapted to the service interval of the unit in order to minimize the out-of-service periods and, on the other hand, eliminating the need, in the case of disposal of used operating fluid in a manner contained within the unit, to change the operating fluid during the life of the unit.